Dilatation catheters are used to dilate body vessels, orifices and conduits such as an artery narrowed by atherosclerotic plaque and/or fibromuscular disease or to dilate a constricted or obstructed ureter or urethra. The prior art devices basically consist of an elongated catheter having an inflatable extensible elastomeric (rubber-like) or non-extensible balloon or bladder, at or near its distal end. A guide wire or other axial support means is often included to improve the torque control or "steerability" of the apparatus.
The major advantage of dilatation catheter use over conventional surgery is that it is less invasive. Nonetheless, the tissue that is stressed is often also subjected to significant trauma. As the bladder expands, it exerts pressure on the surrounding tissue, causing the tissue to compress, deform and expand. The tissue, of course, has an inherent limit of deformability. When the dilation pressure causes the tissue to deform beyond that limit, the tissue tears apart, often to form a jagged wound, with considerable damage, trauma, pain and bleeding. A principal object of the present invention is to provide a dilatation catheter that permits tissue to be stressed, even beyond its limit of deformability, without experiencing uncontrolled tearing and the undesirable conditions associated therewith.
U.S. Pat. No. 4,747,405, issued to Leckrone on May 31, 1988, U.S. Pat. No. 4,669,469, issued Jun. 2, 1987 to Gifford, III, et al., and PCT/U.S. 86/02617 application of Leckrone, published Jun. 16, 1988 are each concerned with atherecotomy devices wherein a balloon is used to position an opening in a casing about an obstruction such as plaque. The balloon does not carry a cutting element to incise tissue but does carry means for disintegrating the plaque which is generally entrapped within a hole in the casing. The balloon basically positions the hole in the casing up against and about the plaque. Thus, the balloon is not symmetrically located within the blood vessel, an outward cutting element is not present and the blood vessel is not torn by the dilation force.
U.S. Pat. No. 4,799,479, issued Jan. 24, 1989 to Spears, shows use of a balloon to open up an artery and then utilizes a laser, heated wire mesh, or the like, to heat up blood trapped between the mesh and the plaque so that dilation will be maintained and so that a smooth wall will result.
U.S. Pat. No. 4,273,128, issued Jun. 16, 1981 to Lary, teaches the use of a balloon with a knife blade, or a series of knife blades, longitudinally distally removed from the balloon.
Soviet Patent 599802 published in 1976 utilizes a balloon which is located within a tube. When the balloon is extended this forces a cutting element through a window in the tube to accomplish fenestration. Pressure is not exerted on body tissue as the bladder is within the tube.
German Patent 3,402,573 is concerned with a single lumen multi-purpose catheter with an extensible elastic balloon with a cutting facility for treatment of stenosis. This patent utilizes three balloons of equal size at the distal end of the catheter. Each elastomeric balloon carries small cutter elements which extend in the longitudinal direction and which are held in a trough made of hard rubber or plastic. Prior to use the cutters lie hidden in longitudinal slots of the relatively thick wall of the one-lumen catheter. Threads anchor the plate when the balloons are inflated thereby limiting the degree of penetration of adjacent plaque (and possibly tissue).
U.S. Pat. No. 4,484,579, issued to Meno, et al, Nov. 27, 1984 is concerned with a commissurotomy catheter which serves for separating fused heart valve leaflets. The device includes four balloons carried by a single catheter structure. In use the device fits through the valve with two balloons on each side of the valve. A nylon or similar string is attached between the pairs of balloons on each side of the valve. The balloons can be alternately expanded and contracted thereby causing the strings strung between each pair of balloons to saw or pulsate into fused portions of the heart valve leaflets and separate them. The actual cutting portion of the string is not carried on the exterior of the balloons.
U.S. Pat. No. 4,660,560, issued Apr. 28, 1987 to L. A. Klien discloses an apparatus for relieving obstruction of the urinary tract caused by an enlarged prostate gland. A balloon is inserted via a urethral catheter and then is expanded until the prostate has been forced back from around the urethra. The apparatus of this patent does not employ a cutter of any sort.
The above-mentioned patents do not make use of a cauterizing (i.e. an electrosurgical or radio frequency surgical) cutting element. Nor do the above discussed patents either suggest or show any advantages for utilizing an inextensible bladder or balloon, i.e., a balloon which is not elastomeric (or elastic) and which can be inflated to only a selected shape and volume and which cannot extend longitudinally when pressurized. Furthermore, the above discussed patents are not concerned with a radially symmetrical, generally cylindrical in shape when expanded, balloon which extends longitudinally along a body passage and a cutting element which extends longitudinally along and generally parallel to the balloon, which balloon creates a substantially uniform tangential tension in tissue being cut, and which cutting element at the same time performs the necessary cutting whereby a clean longitudinally extending incision results and uncontrolled tearing of the tissue does not occur.
In radio frequency electrosurgical cutting a radio frequency current is allowed to pass from an active cutting electrode through a patient's tissue and into a grounding pad or cable. The current cuts tissue at the active cutting electrode, the cutting rate being dependant on current density through the tissue in that area. At low current density heat is generated but no cut is achieved. At high current density fast cutting occurs.
Current density depends on the voltage applied and can be controlled utilizing an adjustment present on a conventional generator utilized for this purpose. The current density also depends on the series impedance of the overall circuit. Series impedance is equivalent to the sum total of the resistance to the current throughout the circuit. It is affected by the material and the design of the active electrode, by the patient, by the type of tissue to be cut, and by the condition of contact established between the patient and the grounding pad as well as by the location of the pad relative to the cutting site. During surgery, the generator setting is usually adjusted to compensate for this variability and to reflect the surgeon's preference. Generators used in this type of surgery have a wide range of power output to accommodate a variety of procedures and devices. For example, the generator can be adjusted to cut tissue, or to cauterize adjacent already cut or torn tissue, or to do both.
The objective in electrosurgical cutting is to heat the tissues cells so rapidly that they explode into steam leaving a cavity in the cell matrix. The heat is meant to be dissipated in the steam and to not conduct through the tissue to thereby dry out adjacent cells. When the electrode is moved and fresh tissue is contacted new cells are exploded and the incision is made. Such electrosurgical cutting involves the sparking of the current to the tissue. The current utilized is in the radio frequency range and operates by the radio frequency current jumping across an air gap to the tissue. This is known as sparking.
An explanation of electrosurgical cutting theory can be found in the SSE3B Instruction Manual published by Valleylab of Boulder, Colo. on Apr. 1, 1979.
An advantage of electrosurgical cutting, particularly if it is performed utilizing a cutting electrode as disclosed in copending application Ser. No. 522,254, of Buelna, commonly assigned herewith, which is hereby incorporated herein in its entirety by reference, is that overheating of adjacent tissue with accompanying desiccation and damage is limited or prevented. Thus, what one can obtain is a clean cut without damage to adjacent tissue. A clean controlled cut is particularly desirable to assure that tearing does not occur in a direction away from the desired orientation of the cut.
The present invention is directed to overcoming one or more of the problems as set forth above.
Disclosure of Invention
In accordance with an embodiment of the invention a dilatation catheter assembly comprises in combination: an elongated tubular body having a distal end carrying a radially dilatable inextensible longitudinally extending member adapted to be positioned longitudinally along a body conduit and to dilate in a radially symmetrical manner and exert pressure on surrounding body tissue to provide a substantially uniform tangential tension therein; means for dilating the dilatable member to a constant inextensible volume and a cutting element carried on the exterior of the dilatable member that moves radially in concert with the exterior of the dilatable member and is adapted to incise said tissue, thereby reducing damage to said tissue from dilation forces.
In accordance with another embodiment of the invention a dilation catheter assembly comprises an elongated tubular body having a distal end carrying a radially dilatable member adapted to be positioned in body conduit and exert pressure on surrounding body tissue; means for dilating the dilatable member and an electrosurgical cutting element carried on the exterior of the dilatable member that moves radially in concert with the exterior of the dilatable member and that is adapted to incise the tissue, thereby reducing damage to the tissue from dilation forces.
In use the novel catheter of the invention concurrently exerts pressure on the tissue thereby placing it under tension and makes a clean, sharp generally longitudinally extending incision in the tissue while the tissue is subjected to the dilatation forces exerted by the dilating member. The incision allows the tissue to separate along a predetermined path and in a relatively clean, trauma-free manner as compared to the uncontrolled tearing that occurs when using prior devices.
Accordingly, another aspect of the invention is a method for dilating a body conduit, vessel or orifice comprising: inserting thereinto a dilatation catheter assembly comprising an elongated tubular body having a distal end carrying a radially dilatable inextensible member adapted to be positioned in a body conduit and to dilate in a radially symmetrical manner and exert pressure on surrounding body tissue to provide a substantially uniform tangential tension therein and a cutting element carried on the exterior of the dilatable member; dilating the inextensible dilatable member to an extent that causes the tissue to be stressed by the dilatable member; incising the stressed tissue using the cutting member; radially contracting the dilatable member to cause the dilatable member and cutting element to disengage the tissue; and withdrawing the dilation catheter assembly therefrom. The dilating and incising steps are suitably repeated until the dilatable member has reached a desired volume prior to the radial contracting step.
Still another aspect in accordance with the present invention is a method for dilating a body conduit, vessel or orifice. The method comprises inserting thereinto a dilation catheter assembly comprising an elongated tubular body having a distal end carrying a radially dilatable member adapted to dilate and exert pressure on surrounding body tissue and an electrosurgical cutting element carried on the exterior of the dilatable member; dilating the dilatable member to an extent that causes the tissue to be stressed by the dilatable member; activating the electrosurgical cutting element such that the stressed tissue is incised by the cutting element; discontinuing activation of the electrosurgical cutting element; radially contracting the dilatable member to cause the dilatable member and cutting element to disengage the tissue; and withdrawing the dilation catheter assembly therefrom. The dilating and incising steps are suitably repeated until the dilatable member has reached a desired volume prior to the radial contracting step.